RFR: 8352765: G1CollectedHeap::expand_and_allocate() may fail to allocate even after heap expansion succeeds [v2]

[Ivan Walulya]

> Hi,
> 
> Please review this change to ensure that G1 provisions for at least one Eden region after a GC when computing the young length target.
> 
> The issue reported in the CR occurs at the end of a GC, after successfully expanding the heap, an allocation fails because `policy()->should_allocate_mutator_region()` returns false. This happens because the computation did not properly account for young regions already allocated as survivor regions, leading to an Eden region target of zero.
> 
> With this change, we factor in the young regions that have already been allocated as survivor regions and ensure that at least one region is targeted for Eden.
> 
> Testing: Tier 1-3
>               Reproducer in the CR.

Ivan Walulya has updated the pull request incrementally with one additional commit since the last revision:

  Thomas Review

-------------

Changes:
  - all: https://git.openjdk.org/jdk/pull/24257/files
  - new: https://git.openjdk.org/jdk/pull/24257/files/7eea1ee3..041b478c

Webrevs:
 - full: https://webrevs.openjdk.org/?repo=jdk&pr=24257&range=01
 - incr: https://webrevs.openjdk.org/?repo=jdk&pr=24257&range=00-01

  Stats: 7 lines in 1 file changed: 1 ins; 1 del; 5 mod
  Patch: https://git.openjdk.org/jdk/pull/24257.diff
  Fetch: git fetch https://git.openjdk.org/jdk.git pull/24257/head:pull/24257

PR: https://git.openjdk.org/jdk/pull/24257